4 Answers
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The word I hear most is noun adjective, while attributive noun and noun adjunct sound equally appropriate and current. I have never heard noun premodifier, though it sounds technically correct. I might also use adjectival noun myself despite Wikipedia's reservations. A noun adjective is always a modifier, but not the other way around: modifier is a correct but less specific term.

Nouns used in this way are sometimes said to be adjectives or to behave like adjectives. Attributive nouns may be marked in dictionaries with a label like often attrib placed after the part-of-speech label for noun. While any noun may be used attributively, the label is limited to those quite frequently used in this manner. An adjective is defined as a word standing for the name of an attribute which describes a noun more fully, e.g., "yellow flower."